In recent years, there are an increasing number of portable terminals employing touch panels for realizing UIs (User Interfaces) that mainly use soft keys and a reduction in size of the portable terminals is in progress. In employing the touch panels in such portable terminals, a large number of methods for effectively using limited spaces of the touch panels are proposed. For example, there are proposed a method of determining an area in contact with a tablet and generating a soft keyboard when the contact area exceeds a threshold (e.g., Patent Document 1) and a method that can change, without displaying a menu on a screen, an input to a touch panel by applying mode switching operation to an electronic pen (e.g., Patent Document 2).
In order to prevent malfunction of soft keys displayed in a narrow space, there is also proposed a method of calculating a frequency of use of the soft keys by a user and increasing a size of frequently-used soft keys to thereby prevent wrong operation of the user (e.g., Patent Document 3). In order to quickly perform character input operation using as few keys as possible, for example, there are also proposed a method of displaying a soft key character string (e.g., Patent Document 4) and a method of causing a touch pen to come into contact with soft keys when characters are input and inputting a large number of characters to soft key display according to directions for moving the touch pen (e.g., Patent Document 5).
In order to improve operability for users, there are an increasing number of portable terminals in which dedicated devices are provided to allow, when applications run in the background, the users to operate the applications in the background. Such dedicated devices make it possible to save labor and time of the users to switch screens of the applications in order to operate the applications in the background.    Patent Document 1: Japanese Patent Laid-Open No. 11-272423    Patent Document 2: Japanese Patent Laid-Open No. 07-160398    Patent Document 3: Japanese Patent Laid-Open No. 11-265240    Patent Document 4: Japanese Patent Laid-Open No. 2001-84086    Patent Document 5: Japanese Patent Laid-Open No. 2003-157144